I generally use xfce because it runs fast. When I "sudo apt install kate", it asks me to install 300MB dependent library. Same for kdiff3, "sudo apt install kdiff3" requires 300MB dependent library too. However, "sudo apt install kdiff3-qt" only requires 5MB, which is perfect. So please provide an APT install package which does not depends on KDE, similar to kdiff3. Maybe kate-qt???
Seems snap kate package https://snapcraft.io/kate installs lots of dependents binaries too.
Distros provide the packages; you'll need to ask your distro for a different kind of package. However, I'm not sure what's in the kdiff-qt package, but if an app requires a dependent library, it's gonna need to get that library somehow. Options include installing the library separately via the package manager and dynamically linking against it, or bundling the library with the app itself--which means no outside dependencies, but then the app bundle itself is very large. But you have to pay the piper somehow. :) What 300mb dependent libraries does your distro's Kate package require? It almost sounds like maybe you don't already have Qt on your system, and the package manager is going to install it to get Kate.
Thanks. I generally use Xbuntu, (ubuntu with xfce4 only), which by default does not have qt stuffs and KDE. So it requires 250-300MB disk for Kate installation. I just gave a try on a clean Debian 9 VM. Installation of kdiff3 requires 311MB, while kdiff3-qt requires 31MB. I think kdiff3-qt only includes the minimal QT stuffs instead of whole QT. Thanks, anyway. I don't think I will switch to KDE from xfce since xfce runs fast. I will just use Geany instead of Kate as a workaround.